This invention relates to a low profile, low drag, broad-banded antenna system for receiving the circularly polarized signals from an orbiting global positioning satellite.
Orbiting satellites transmit coded signals which, when received and combined with signals from other satellites provide latitude and longitude information of the receiving station. These radio frequency signals are circularly polarized, and have low signal strengths. Any time any one of the satellites is near the horizon, the signal from that satellite is difficult to receive because prior art receiver antenna gain has been generally poor at low angles. Positioning information under those circumstances can be difficult if not impossible to obtain.
Antenna systems normally employed to receive these satellite signals, particularly for aircraft operations, must be capable of receiving the signals from the satellite at any position, either overhead or near the horizon. It is also important that the antenna, which is normally mounted on the upper outer surface of the aircraft, have a low profile design to minimize aerodynamic drag.
There have been several antennas developed to an attempt to receive positioning signals from orbiting satellites. These antennas generally include four antenna elements which are connected through a phase shifting network so that the circularly polarized signals are properly combined. These prior art satellite antennas, however, have not been successful in capturing the signals from the satellite when it is near the horizon.